Latest and Greatest: My Citrix on VMWare

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This may be my last entry on Citrix/VMWare for the time being.

After 1 month of production runs, our 1 vCPU 2GB RAM VMs are churning nicely, averaging around 32 concurrent users. Running at 10 VMs per DELL 2950 Host, we see that Host Memory is stable, Host CPU is well utilized. There is enough capacity that another 2 VMs could potentially be added with no adverse effects, netting approx 380 users per HOST... solid density.

The only questionable item we have seen is paging on the guest level. To combat this, we established another host running 10 VMs configured with 3gb each and a seperate host running 10 VMs with 4gb each.

Early results indicate the 3gb is our "sweet spot." With the same number of users, the 4gb VMs were capping their utilization at 2.8-3.2 GB Used. Also, considering the hosts only have 48gb, consuming 30-36gb (10-12 VMs @ 3gb each) still allows overhead for the host, for vmotion, and any auxilliary or even additional VMs without the risk of oversubscription. The 4gb VMs, although with slightly more horsepower, forces the host to limit to 10 or 11 vms at most, since we want to avoid over subscription.

In summary:
10 x 2gb VM -- increased CPU due to paging, no other problems. Potential for 15+ VMs
10 x 3gb VM -- less paging. Potential for 12-15 VMs, based on total resource consumption
10 x 4gb VM -- solid performance, but peaked memory just over 3gb. 10-11 VMs max per host

Please note, this is within our framework with our specific custom application. One caveat of the 4gb servers is we did NOT increase the load evaluator, so the number of users was still capped. Increase the user load may allow for more users per VM to leverage the additional RAM.

Early Returns: 3gb looks to be the optimal configuration for this environment based on user load, vm performance, and esxtop results. It would also maintian the focus of scaling out instead of scaling up.

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Follow up: Unfortunately, this will be my last post for this specific case study. I am moving on to different projects with a different company. However, I will post new case studies and update this study if and when I receive any additional results.